Single cell assays to measure signal transduction and other cellular processes are useful for the identification of drug targets, as well as for drug screening. The number of known signaling molecules involved in particular cell functions and disease states is rapidly increasing. At the same time, combinatorial chemistry has dramatically expanded the number of substances that must be tested for their effect on specific signaling molecules and transduction pathways. Commonly used in vitro measurements of drug-target binding interactions and other screening methods are often inadequate to assess the effectiveness of drugs within the cellular context, and therefore, the ability to assay intact cells for particular cell functions would be a powerful way to investigate all signaling steps that lead to the monitored event. Currently, the main limitations for this strategy are: (i) the lack of an efficient method to rapidly introduce membrane impermeant molecules into adherent cells using cost efficient amounts of samples and (ii) the limited number of available single cell assays to test for particular cell functions.